Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology may use a plurality of electrostatic actuators, piezoelectric actuators, or thermal actuators to eject ink from a plurality of nozzles in an aperture plate. In electrostatic ejection, each electrostatic actuator, which is formed on a substrate assembly, typically includes a flexible diaphragm or membrane, an ink chamber between the aperture plate and the membrane, and an air chamber between the actuator membrane and the substrate assembly. The electrostatic actuator may further include an actuator electrode formed on the substrate assembly. When a voltage is applied to activate the actuator electrode, the membrane is drawn toward the electrode by an electric field and actuates from a relaxed state to a flexed state, which increases a volume of the ink chamber and draws ink into the ink chamber from an ink supply or reservoir. When the voltage is removed to deactivate the actuator electrode, the membrane relaxes, the volume within the ink chamber decreases, and ink is ejected from the nozzle in the aperture plate.
The membrane may occasionally be drawn too far toward the electrode when, for example, the voltage applied is too great, or the voltage is applied for too long. This may cause the membrane to suddenly deform, and the membrane may contact the electrode resulting in a short. This is referred to as a “pull down.” When the membrane contacts the electrode, a small discharge can cause an arc or plasma that vaporizes metal locally leading to undesirable behavior. A low ohmic contact may result in a large current that causes similar damage to arcing, but may also lead to trace failure or ASIC damage.
An electrostatically actuator for an ink jet printhead that overcomes problems associated with pull downs would be desirable.